Low power consumption is required of a semiconductor storage device including a nonvolatile memory. In particular, in a semiconductor storage device to be introduced into a battery-operated mobile device such as a portable device or the like, the requirement is high, and various power consumption reduction schemes are now being examined. As an example, in a semiconductor storage device, it is known that the influence on a battery of the degree of power consumption during an idle period when there is no host access is great, and low power consumption during an idle period is therefore now being examined.
On the other hand, the performance of the semiconductor storage device is high, an ASIC (Application Specific Integrated Circuit) forming the semiconductor storage device is large in the present circumstances, and battery consumption due to leakage current is unignorable even in a non-operating state.
In order to realize low power consumption, although power-off of the semiconductor storage device during an idle period is conceivable, in this case, the time necessary for a host to obtain the access-enabled state becomes longer when the host is to carry out access. Furthermore, the power of the memory in which management data is stored is also turned off, and hence it is necessary to write the management data stored in the memory to a backup nonvolatile memory. Under such circumstances that the power is frequently turned off, the rewriting amount of the nonvolatile memory is increased by the backup processing, and the reliability of the nonvolatile memory is lowered.